Social structure of short-finned pilot whales

Since the early 80s of the last century researchers have studied the social structure of short-finned pilot whales. Mostly, they used the non-invasive photo-identification technique (...here...) in order to document relationships between free-ranging animals at sea. They photographed individuals of distinct groups and compared association patterns between individuals. Short-finned pilot whales were shown to live in stable social groupings and are believed to form matrilinear kinship groups. Within such groups all individuals are genetically related with the oldest female and mating occurs between individuals from different groups.

Click ...here... to see a large group meeting underwater
(.mov file with 8.6 MB) with more than 25 individuals.

Click ...here... to see a pilot whale subgroup with a newborn (.mov file with 2.6 MB). This newborn still has fetal folds and is closely related with its mother.

Madeira
From 2003 to 2011 Filipe Alves and colleagues photo-identified 364 individuals south and east off Madeira island. 85 animals were re-sighted during 1-8 successive years. The mean group size was 18 individuals and ranged 2-60. They found a population consisting of long-term resident, regular visitor and transient groups. By further using molecular genetics techniques, the researchers found genetic relatedness between group individuals. Combined with their observation that individuals from different groups temporarily associate, this suggests that short-finned pilot whales form matrilinear kinship groups and mating might occur between individuals of different groups.

Tenerife, Canary Islands

From 1991 to 1992 Jim Boran and Sara Heimlich photo-identified 495 short-finned pilot whales within 46 pods southwest off Tenerife. Based on patterns of occurrence, the area is frequented by visitor and resident groups. It was found that during meetings of different groups, the highest ranked associations of reproductive females were with males from other pods suggesting that mating occurs between individuals of different pods. These findings show parallels to the social structure of matrilinear pods of resident killer whales.

Pacific coast of Japan

From 1986 to 1987 Tomio Miyashita, Toshio Kasuya and Kyoichi Mori photo-identified at least 101 free-ranging short-finned pilot whales off the Pacific coast of Japan. However, this was a feasibility study and did not reveal insights into long-term social affiliations. Further research from Toshio Kasuya and Helene Marsh on sympatric groups suggests that their social structure resembles group structures observed for cetacean species living in matrilineal kinship groups.

Big Island, Hawaii

From 1985 to 1988 Susan Shane and Dan McSweeney photo-identified short-finned pilot whales off the island of Hawaii. They found that 30 whales were sighted two or more times and 30 whales were identified between seasons. Data indicated a degree of pod cohesiveness and individual adult males did not associate with the same pod all the same time. Comparable to the analysis of the data obtained off California, pilot whale pods in Hawaiian waters are fairly stable.

Santa Catalina Island, California

From 1983 to 1986 Susan Shane and Dan McSweeney photo-identified short-finned pilot whales in waters off Santa Catalina Island. They resighted 32 whales on two or more days, and 15 during two or more seasons. Their association patterns indicated a degree of social affiliation between some individuals and it is suggested that pilot whale pods are fairly stable. Individual adult males did not associate with the same pod all the same time.